A liquid crystal display device is known as a typical example of a display device. A liquid crystal display device has a plurality of liquid crystal elements, and the liquid crystal elements have a pair of electrodes (pixel electrode, counter electrode) and a layer (liquid crystal layer) of compounds (liquid crystal molecules) having liquid crystallinity interposed therebetween as a basic structure. Polarized light incident to the liquid crystal layer through one of a pair of polarization plates arranged so as to sandwich the liquid crystal elements is output through the other polarization plate after the polarization plane thereof is rotated by the liquid crystal layer. The rotation of the polarization plane is determined by the orientation of the liquid crystal molecules in the liquid crystal layer. By forming an electric field in the liquid crystal layer using a pair of electrodes, the liquid crystal molecules change from an initial orientation state to an orientation state determined by the electric field. As this orientation state changes, transmissivity of the liquid crystal elements changes, and a gradation display is realized.
In the region in which display is performed (display region), by applying an appropriate electric field to the liquid crystal layer according to the gradation displayed, a high-quality display can be performed. The liquid crystal layer is usually sealed between a pair of electrodes by a seal. However, when impurities such as metal ions and inorganic anions, or organic acids penetrate into the liquid crystal layer from the outside, an appropriate electric field cannot be maintained due to these impurities, causing display defects such as display speckles and burn-in. A trap electrode arranged to prevent ionic impurities from entering the liquid crystal layer outside the display area has been disclosed as a countermeasure against these display defects in Japanese Laid-Open Patent Publication 2009-265484 and Japanese Laid-Open Patent Publication 2016-71228.